The invention relates to an articulated lever cutting and forming press consisting of a single or multiple press stand and one or more frame-shaped press slide(s) which as a rule is or are closed. The slide or slides possesses--in each case between two symmetrically identical articulated lever systems with their joints bending toward the center of the press--a hydraulic cylinder drive which is arranged on the slide and whose piston is connected, at the end of its piston rod, to the multi-articulated support guided in the center of the press in the slide. The piston is also connected to at least two connecting rods which are movably arranged on the said support. At the other end the connecting rods, engage the articulated lever systems which in turn on the one hand are arranged on the press frame so that their height can be adjusted and on the other hand are rotatably mounted in the slide and directed toward the press table, the hydraulic cylinder drive obeying the relationship that the piston stroke is equal to the path covered by the multi-articulated support minus the slide stroke.
West German Patent No. 2,925,416 has disclosed a toggle lever sheet metal cutting press of this type. It has become widely established in practice under the name "differential displacement press" since not only does it have convincing technology, which, inter alia, achieves a substantial reduction in the acceleration forces, but furthermore at least one serious problem of industrial hygiene is reduced by the embodiment described at the outset.
The object of this Patent is based on the fact that hydraulic fluid is invariably not completely incompressible and the resulting volume difference is equal to the product of volume under atmospheric pressure.times.the working pressure and the compression index (about 70.times.10.sup.-6), to which volume difference it is necessary to add the volume reduction due to the finely dispersed air inclusions frequently present. The result of this is that, when the pressure is suddenly relieved, i.e. when the material to be cut is parted by the slide carrying the cutting tool, the resulting expansion volume is not insignificant and, in cooperation with the elastic expansion behavior of all guide paths of the hydraulic press which are executed under pressure, through expansion and spring mounting of the machine frame and in conjunction with the residual slide movement which is uncontrollable at this moment, leads to the known cutting impact noise, i.e. the "cutting report".
The result obtained according to this Patent means that, when the hydraulic cylinder drive is arranged on the slide, the stroke of the hydraulic cylinder drive is smaller than in the case of a comparable prior art press, in which the hydraulic cylinders are supported on the press stand.
This substantially reduces the hydraulic fluid volume to be transported and subjected to a load at the end of the working process, and hence substantially reduces the possible expansion volume, with the result that the cutting impact noise is greatly reduced in accordance with the object.
Further advantages of an embodiment according to the Patent described at the outset are, inter alia, the repeatability of the hydromechanical drive, which has a tolerance of only +/- 0.01 mm at bottom dead center, and inevitably lead to the object of widening the field of uses of these presses.
The Patent is based on U.S. Pat. No. 2,087,811 and on British Patent No. 804,352. In these embodiments, the stroke of the stationary drive cylinder fixed to the frame is determined by the transmission ratio resulting from the toggle lever drive and the type of connecting rods in a conventional manner.
Regarding the form of the stand, reference may be made to Makelt, Carl Hanser Verlag Munich 1961, page 33, FIG. 23 ("The mechanical presses"). This publication describes the load and deformation conditions in the closed, rectangular twin-stand frame of a vertical press. This is a statically multiply indeterminate system in which the force P acts at the center of the press support (center of table) and its opposing forces P/2 act at the two crankshaft bearings at a distance W from the axis through the center of gravity of the stand. The greatest sag occurs at the center of the table at the point of action D of the force P.
The relationships arising from these loads with regard to the course of the bending line and the determination of the spring mounting of the frame will not be repeated individually here; instead, it will merely be pointed out that the unsupported length will finally be determined by the actual spring mounting of the frame in conjunction with the given load.
So-called "C frames" cannot generally be used for presses according to the definition given at the outset, since their frame spring mounting greatly influences the accuracy of cutting in presses having a high load capacity.